Hormonal Mechanisms for Parental Control

派：道格拉斯·W·莫克，共同派：休伯特·G·施瓦布IBN-9604370近年来，父母平等对待所有子女的普遍假设受到了质疑。在许多动植物群体中，父母生育的后代数量比通常完全支持的要多，这迫使随后的家庭规模向下调整。父母生产过剩的根本原因来自环境不可预测性的多个来源(包括资源不可预测性、后代的意外损失、部分幼崽的捕食、家庭成员或其他人的自相残杀等)，但这一事实同时产生了兄弟姐妹竞争，这促使父母产生等级关系，以将这种竞争的成本降至最低。因此，父母赋予一些后代特殊的优势和/或给予其他所谓的边缘幼崽成员障碍。生物学上父母偏爱的最好表现可能是许多捕食性鸟类的异步化孵化。在那里，早期孵化为第一次下蛋的胚胎提供了一个发育的起点，这有助于它们在随后的任何兄弟姐妹争夺有限食物的竞争中取得成功。休伯特·施瓦布S最近发现，随着产卵过程的进行，雌性实验室金丝雀在蛋黄中积累了越来越多的睾丸素，这为父母操纵后代维加提出了一种新的机制，并启发了从牛鹭(BuBulcus Ibis)身上收集新鲜卵子的灵感，牛鹭是一种已知的具有致命兄弟姐妹攻击(或兄弟姐妹杀戮)的物种。这个物种边缘的第三个蛋含有的蛋黄睾丸素(加上两个类似的类固醇)比它的两个筑巢伙伴的蛋要少得多，后者通常提前1-3天孵化。白鹭的模式(类固醇剂量递减)与金丝雀完全相反，但与孵化异步化的影响一致，这一事实表明，激素沉积到蛋黄中可能是一种广泛而灵活的亲代适应，以操纵雏鸟内部的竞争动态和生存。拟议的研究旨在通过两项实地研究来探讨这一问题。首先，将通过向最后产卵的鸡蛋中注入不同水平的3-类固醇鸡尾酒来实验操纵黄鹭系统，然后测量孵化后的幼崽在野外条件下的竞争行为(乞讨和打斗)。如果操纵类固醇是父母管理兄弟姐妹竞争的进化策略的一部分，那么拥有增强的最后一个卵子的幼崽应该表现出不断升级的争斗和乞讨，最终损害父母的利益。其次，为了测试母亲S减少类固醇的使用是否是一种普遍现象，是否与同胞竞争特别激烈的家庭有关，将对其他杀死兄弟姐妹的物种进行探索性调查，每个物种都与一个关系密切但没有攻击性的姐妹物种配对。就像牛白鹭的试验工作一样，一产下一窝蛋就会被收集起来，它们的蛋黄被冷冻起来，供以后进行类固醇含量的实验室分析。通过这项工作，我们希望增加对父母在自然条件下的生殖策略的了解，并确定母亲服用类固醇是否是增强父母健康的一般机制。

PI: Douglas W. Moc, CO-PI: Hubert G. Schwabl IBN-9604370 In recent years, the general assumption that parents value all of their offspring equally has come into question. In many animals and plant groups, parents produce greater numbers of concurrent young than can ordinarily be supported fully, forcing a subsequent adjustment downward in family size. The underlying reasons for parental overproduction stem from multiple sources of environmental unpredictability (including resource unpredictability, accidental losses of progeny, partial-brood predation, cannibalism by family members or others, ect.), but the fact of it simultaneously generates sibling rivalry, which creates incentives for parents to produce a hierarchical sibship to minimize the costs of such rivalry. Thus, parents confer special advantages on some offspring and/or handicaps on other, so called marginal brood members. The best-studied manifestation of biological parental favoritism is probably asynchronous hatching in many predatory birds species. There, early onset of incubation gives embryos in the first- laid eggs a developmental head-start that facilitates their success in any ensuing sibling competitions for limited food. Hubert Schwabl s recent discovery that female laboratory canaries deposit increasing amounts of testosterone into yolks as the laying process proceeds suggested a new mechanism for parental manipulation of offspring vigar and inspired the collection of fresh eggs from cattle egrets (Bubulcus ibis), a species known to practice fatal sibling aggression (or siblicide ). The marginal third egg of this species contained much less yolk testosterone (plus two similar steroids) than those of its two nestmates, which normally hatch 1-3 days earlier. The fact that the egret pattern (decreasing steroid dose) is exactly opposite that found in canaries, but congruent with the effects of hatching asynchrony, suggests that hormone depositions into yolks could be a widespread and flexible parental adaptation for rigging intra-brood competitive dynamics and survival. The proposed study aims to explore this matter through two field studies. First, the cattle egret system will be experimentally manipulated by injecting various levels of a 3-steroid cocktail into last-laid eggs, then measuring the subsequent competitive behaviors (begging and fighting) of the hatchlings under field conditions. If steroid-manipulation is part of an evolved parental strategy for managing sibling competition, broods with boosted last- eggs should show escalated fighting and begging, ultimately to the detriment of parental interests. Second, to test whether the mother s cutback on steroids is a general phenomenon and associated with families in which sib- competition is especially keen, an exploratory survey will be made of the other siblicidal species, each paired with a closely-related but nonaggressive sister species. As with cattle egret pilot work, clutches of eggs will be collected as soon as each is laid, their yolks frozen for later laboratory assays of steroid content. Through this work, we expect to increase understanding of the reproductive strategies of parents under natural conditions and to determine whether maternal steroid dosing is a general mechanism used to enhance parental fitness.